Vessel comprising a lifting device

ABSTRACT

A vessel for installing a platform on an offshore support structure comprises a floating body, a lifting device which is tiltable about a tilting axis with respect to the floating body and a tilting force member for applying a tilting force to said lifting device. The lifting device is provided with a static part that is tiltable about the tilting axis and a movable part which is movable in vertical direction with respect to the static part. The tilting force member engages a drive location at the static part.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a national stage filing of Internationalpatent application Serial No. PCT/NL2012/050410, filed Jun. 13, 2012,and published as WO 2012/173472 A1 in English.

BACKGROUND

The discussion below is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter.

Aspects of the invention relate to a vessel for installing a platform onan offshore support structure, comprising a floating body, a liftingdevice which is tiltable about a tilting axis with respect to thefloating body and a tilting force member for applying a tilting force tothe lifting device, which lifting device is provided with a static partthat is tiltable about said tilting axis and a movable part which ismovable in vertical direction with respect to the static part.

Installing and removing a module on or from an offshore supportstructure is known as a float-over operation. Usually, the offshoresupport structure is fixed to the seabed. A lifting device lifts asea-going platform and sets it down on the support structure. After theplatform is seated upon the support structure the lifting device islowered further and the vessel leaves the location of the supportstructure. In practise the floating body will be subject to wave motionsat open sea. As a consequence, the floating body will be moved invertical and horizontal directions. During transferring the platform tothe support structure the platform should be kept in a stable positionwith respect to the support structure. This is performed inter alia bycompensating the horizontal movements of the floating body throughdisplacing the platform relatively to the floating body by means of atilting force member comprising a hydraulic cylinder. A disadvantageexists in that the hydraulic cylinder for horizontal compensation limitsa large displacement of the platform in vertical direction.

SUMMARY

This Summary and the Abstract herein are provided to introduce aselection of concepts in a simplified form that are further describedbelow in the Detailed Description. This Summary and the Abstract are notintended to identify key features or essential features of the claimedsubject matter, nor are they intended to be used as an aid indetermining the scope of the claimed subject matter. The claimed subjectmatter is not limited to implementations that solve any or alldisadvantages noted in the background. An aspect of the inventioncomprises a flexible lifting device in terms of freedom of movement.This is achieved by a vessel of which a tilting force member engages adrive location at a static part. Under operating conditions the tiltingforce member can exert a tilting force on the drive location of thestatic part of the lifting device so as to tilt the lifting device withrespect to the floating device or to limit tilting of the lifting devicewith respect to the floating device.

The advantage of the vessel is that the tilting force member and thedisplacement of the movable part with respect to the static part arefunctionally decoupled. As a consequence, the lift height is independentfrom the tilting force member, which makes the lifting device flexiblein respect of freedom of movement. It is noted that the static part is astatic or non-movable portion of the lifting device when considering thestatic part and the movable part only, but as described hereinbefore thestatic part is tiltable with respect to the floating body.

The movable part is moved in horizontal direction upon tilting thestatic part by means of the tilting force member. This provides theopportunity to compensate horizontal movements of the floating bodyduring installing a platform when the platform is supported by themovable part of the lifting device.

In a preferred embodiment the drive location is located below thetilting axis. This provides the opportunity to locate the tilting forcemember at a low position with respect to the lifting device, for exampleclose to the floating body. This may create a relatively large freespace at an upper portion of the lifting device.

In a practical embodiment a support member for supporting a platform maybe pivotally mounted to the movable part. The advantage of thisconfiguration is that during a tilting motion of the lifting device thesupport member may stay in the same position with respect to theplatform that is supported.

The static part may be tiltable through a ball joint such that themovable part can be displaced in all horizontal directions. In this casean infinite number of tilting axes extending through the center of theball joint are present. The displacement may be supported by a tiltingforce member which is adapted such that it can displace the drivelocation in different horizontal directions.

The tilting force member may comprise a drive unit so as to activelycontrol the force of the tilting force member exerted on the staticpart. In this case the tilting force member may be called an activemember. In practice the drive unit may comprise at least two hydrauliccylinders which are operable in mutually different directions, forexample perpendicular to each other.

Alternatively, the tilting force member comprises a resilient element.In this case the tilting force member may be called a passive member.The resilient element may be a spring, a rubber element or the like. Thetilting force that is exerted by the tilting force member on the staticpart is then dependent on inter alia the stiffness of the resilientelement.

The static part and the movable part may be formed by a hydrauliccylinder. Preferably, the hydraulic cylinder can be controlled such thatthe movable part is retracted quickly. This minimizes the risk of acollision between the lifting device and the platform during retractingafter the platform has been transferred to the support structure and thevessel is free from the platform.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will hereafter be elucidated with reference tothe schematic drawings showing an embodiment of the invention by way ofexample.

FIG. 1 is a perspective view of an embodiment of a vessel.

FIG. 2 is a schematic side view of a lifting device of the embodiment asshown in FIG. 1.

FIG. 3 is a perspective view of the embodiment as shown in FIG. 2.

FIG. 4 is a schematic side view of a second embodiment of a liftingdevice.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows an embodiment of a vessel 1. The vessel 1 is used forinstalling a sea-going platform 2 on an offshore support structure 3.The platform may be a drilling unit, a production unit, a high voltagestation or the like. The support structure 3 rests on the seabed and thevessel 1 including the platform 2 is brought into a position directlyover the support structure 3.

The vessel 1 comprises a hull or a floating body 4 on which a pluralityof lifting devices 5 are mounted. The lifting devices 5 carry theplatform 2. FIGS. 2 and 3 show an embodiment of one lifting device 5 inmore detail. The lifting device 5 is provided with a static part 6 and amovable part 7. The static part 6 is tiltable with respect to thefloating body 4 about a tilting axis. The static part 6 is tiltablethrough a ball joint 8. This means that the tilting axis extends indifferent horizontal directions and in fact the ball joint has aninfinite number of tilting axes. In this embodiment the ball joint 8 isformed by a spherically shaped member which is supported by sphericalportions of supporting elements 9 which are attached to the floatingbody 4.

The static part 6 and the movable part 7 are formed by a hydrauliccylinder. Upon operating the hydraulic cylinder the movable part 7 ismoved in vertical direction with respect to the static part 6.

Under operating conditions the lifting device 5 can be tilted withrespect to the floating body 4 by means of a tilting force member. Inthe embodiment as shown the tilting force member comprises two pairs ofopposite hydraulic cylinders 10 as a drive unit. Both pairs of cylindersextend perpendicularly with respect to each other. As a consequence, themovable part 7 of the lifting device can be displaced in all horizontaldirections. Since the movable part 7 is also displaceable in a verticaldirection with respect to the static part 6 the movable part 7 isdisplaceable within a three-dimensional coordinate system.

Driven sides of the hydraulic cylinders 10 of the tilting force memberpivotally engage a drive location 11 at the static part 6 and stationarysides thereof are pivotally mounted to the floating body 4. In theembodiment as shown in the drawings the drive location 11 is locatedbelow the tilting axes of the ball joint 8. The static part 6 functionsas a lever; depending on the dimensions of the parts of the liftingdevice 5 the relative displacements of the movable part 7 and the drivelocation 11 can be selected.

The lifting device 5 is further provided with a support member 12 forsupporting the platform 2. The support member 12 is pivotally mounted tothe movable part 7 by means of a ball joint 13, as well. In theembodiment as shown the support member 12 has a substantially flat uppersurface which can be kept more or less horizontally when the vessel 1including the platform 2 is on open sea and the lifting device 5 isoperated to compensate for movements of the floating body 4 due towaves.

In an alternative embodiment the tilting force member may functionpassively. For example, the drive unit or hydraulic cylinders 10 of theembodiment as described hereinbefore may be replaced by one or moreresilient elements 10′ (FIG. 4). A spring or rubber material as aresilient element are conceivable.

The invention is not limited to the embodiment shown in the drawings anddescribed hereinbefore, which may be varied in different manners withinthe scope of the claims and their technical equivalents. It isconceivable that the drive location is present above the ball joint, forexample. Furthermore, the vessel may comprise a pontoon on which acrane, for example a land crane, is supported through the lifting devicesuch that the position of the crane can be stabilized with respect to anoffshore structure that has a fixed position on the seabed.

1. A vessel for installing a platform on an offshore support structure,comprising a floating body. a lifting device on the floating body whichis tiltable about a tilting axis with respect to the floating body and atilting force member configured to apply a tilting force to said liftingdevice, which lifting device is provided with a static part that istiltable about said tilting axis and a movable part which is movable ina vertical direction with respect to the static part, wherein thetilting force member engages a drive location at the static part.
 2. Thevessel according to claim 1, wherein the drive location is located belowthe tilting axis.
 3. The vessel according to claim 1, wherein a supportmember for supporting a platform is pivotally mounted to the movablepart.
 4. The vessel according to claim 1, wherein the static part istiltable through a ball joint.
 5. The vessel according to claim 4,wherein the tilting force member is configured such that it displacesthe drive location in different horizontal directions.
 6. The vesselaccording to claim 1, wherein the tilting force member comprises a driveunit.
 7. The vessel according to claim 5, wherein the drive unitcomprises at least two hydraulic cylinders which are operable in mutualdifferent directions.
 8. The vessel according to claim 1, wherein thetilting force member comprises a resilient element.
 9. The vesselaccording to claim 1, wherein the static part and the movable part areformed by a hydraulic cylinder.
 10. A vessel, comprising: a floatingbody; a lifting device mounted to the floating body, the lifting devicecomprising a static part and a movable part movable in a lineardirection relative to the static part, the static part being mounted tothe floating body so as to be tiltable about a tilting axis with respectto the floating body; and a tilting force member mounted to the floatingbody and mounted to a drive location on the static part, the tiltingforce member configured to apply a driving force to the static part totilt the static part.
 11. The vessel according to claim 10, wherein thedrive location is located below the tilting axis.
 12. The vesselaccording to claim 10, wherein the static part is tiltable through aball joint.
 13. The vessel according to claim 12, wherein the tiltingforce member is configured such that it displaces the drive location indifferent horizontal directions.
 14. The vessel according to claim 10,wherein the tilting force member comprises a drive unit.
 15. The vesselaccording to claim 10, wherein the tilting force member (10) comprises aresilient element.
 16. A lifting assembly, comprising: a supportingelement; a lifting device comprising a static part and a movable partmovable in a linear direction relative to the static part, thesupporting element being joined to the static part and configured toallow the static part to be tiltable about a tilting axis tosubstantially vertically positions when the supporting element islocated on a horizontal support surface; and a tilting force memberjoined to the static part at a drive location and configured to tilt thestatic part.
 17. The lifting assembly according to claim 16, wherein thedrive location is located below the tilting axis.
 18. The liftingassembly according to claim 16, wherein the static part is tiltablethrough a ball joint.
 19. The lifting assembly according to claim 16,wherein the tilting force member comprises a drive unit.
 20. The liftingassembly according to claim 16, wherein the tilting force membercomprises a resilient element.